On 10/03/2014 1:32 AM, David Litke wrote:
Hello, I am fairly new to mapping towns in Africa, but would like to help out on this project, especially since it is a water-related project and I am a hydrologist. I have a few comments/questions:
As a new mapper relatively unfamiliar with Africa, I cannot stress the importance of any on-the-ground information that can be made available about how to interpret imagery. Otherwise, how can I guess what I am looking at? For example, in the Bassikounou imagery, what are these strange (sometimes very large) white spots (sometimes in the shape of a bow-tie), for example at 15.8604986, –5.9610567? Some kind of tent? Buildings, walls and roads: I can understand the importance of a good base map to the ICRC so they can use it for on-the-ground surveys of water-development information.
[PTT] That square has the look of an institution (health centre or school). Anyway, I would surmise that is a fairly new permanent piece of construction financed from abroad.
Intermittent ponds: Since this is very dry country, it seems to me that we happen to have imagery taken after a fairly strong thunderstorm event (like the one seen at the nearby refugee camp in 2012 <http://intersos.org/en/bulletin/news/malian-refugee-camps-under-water-floods>), and the water we see is essentially puddles left over from this storm., which will be very temporary in duration. What we are mapping essentially are the low spots in the topography where the water collects. I do not believe this has any relation to where groundwater is located. If the ICRC is interested in topography, they might be better off using SRTM elevation data – this also could be processed to find possible dry river and stream channels.
[PTT] In Mali, it was obvious where standing water persisted throughout the year from the darkness of the vegetation relative to surroundings. I mapped such areas because of their impact on roads (generally have to bypass) and farming use.
Trees: Are these Acacia trees? Since it is quite time consuming to map these, is it proven that the tree density is indicative of water availability?
[PTT] You can quickly map trees by creating one node, then copying the node (click on it and select copy from the edit menu), then clicking on each successive tree location and doing paste. My purpose in mapping trees was just to provide landmarks for navigating through the town streets. Sometimes away from town a cluster of trees will be a meaningful indication of water (e.g., oasis).
Wells: Although we are not mapping wells, I was very interested in the email thread about wells (in Mali). I am very surprised that wells can be located by looking at imagery. It seems that only a small fraction of wells could be discernable, mostly only those that have paths converging at the well, or by the animal tracks made by oxen pulling up the buckets. It is very interesting to learn about these animal track patterns though – the length of the animal tracks might be used as to estimate the (maximum) depth to water). Dave *From:* Severin Menard <mailto:[email protected]> *Sent:* Thursday, March 06, 2014 10:14 AM *To:* [email protected] <mailto:[email protected]> *Subject:* [HOT] Mapping Bassikounou, Mauritania - ICRC request Hi, ICRC requested us to map an AOI (Area Of Interest) around Bassikounou, a town close to the border with Mali, for a development project about drinkable water. The approach is the same than for Walikale in DRC. To know more: http://tasks.hotosm.org/job/447 As you can see, I added a banner to make clear what the job is from, for and about. For sure HTML and wording could be improved, please make suggestions. The map features are a bit more various than usual (eg intermittent ponds - please find a link provided by the local Watsan specialist tp have an idea how to identify them on Bing imagery - and trees). I also added a picture and a video of Bassikounou that I found in the web, to have a better idea of what look like the streets and the outskirts. Sincerely, Severin ------------------------------------------------------------------------ _______________________________________________ HOT mailing list [email protected] https://lists.openstreetmap.org/listinfo/hot ------------------------------------------------------------------------ <http://www.avast.com/> This email is free from viruses and malware because avast! Antivirus <http://www.avast.com/> protection is active. _______________________________________________ HOT mailing list [email protected] https://lists.openstreetmap.org/listinfo/hot
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